An intense interest has arisen in fermentation and gasification of carbohydrate-rich biomass to provide alternatives to petrochemical sources for fuels, livestock feeds and for organic chemical precursors. Lignocellulosic biomasses including industrial and agricultural wastes have proved particularly interesting as carbohydrate sources. For lignocellulosic biomasses, pretreatment is generally required in order to separate lignin and hemicellulose from cellulose fibers and thereby increase catalytically effective access of hydrolytic enzymes. A variety of pretreatment processes have been reported, many of which rely on high temperature treatments at high pressures. For review, see ref. 1 and 2.
Discharge of pretreated biomasses from high pressure regions to subsequent processing at lower or atmospheric pressure presents a technical problem that has previously been solved by two general approaches. Particle pumps suitable for semi-continuous processing have been developed that provide pressure sealed-transfer of biomass from regions of different pressure. See for example, WO 03/013714, which is hereby incorporated by reference in entirety. Alternatively, in batch processing, discharge of pretreated biomass from high pressure regions has been achieved using “steam explosion,” where biomass is literally blown out of a pressure treatment device into a blow tank. See for example U.S. Pat. No. 6,506,282. Previous solutions to the “discharge” problem have generally not been suitable for continuous biomass processing. In production scale, continuous processing is advantageous with respect of semi-continuous or batch processing in that the size of equipment can be reduced considerably, for example, between a factor of 2 and 5. Energy losses can also be minimized and troublesome energy pulses avoided through continuous processing.
Improvements of lignocellulosic biomass pretreatment processing are advantageous that reduce costs, particularly energy costs, or otherwise facilitate scale-up to production scale use.
We here describe devices and methods for discharging pretreated biomass from higher to lower pressure regions that are suitable for use in continuous biomass processing. Preferred embodiments provide reduced loss of steam from pressurized pretreatment regions, reduced energy consumption and simplified construction, relative to methods and devices known in the prior art.